Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

During a sheet-through operation, for a first original, a shading
operation is performed to acquire white data and a light-quantity
measuring operation is performed to acquire a reference value. For
subsequent originals, only the light-quantity measuring operation is
performed to acquire a subsequent light quantity. If the reference value
and the subsequent light quantity differ greatly, the shading operation
is performed at this time point to acquire new white data. The
sheet-through operation is not stopped when the shading operation is not
performed and the sheet-through operation is stopped when the shading
operation is performed.

Claims:

1. An image reading apparatus comprising:a scanner unit configured to scan
an original and acquire image data;an original tray for stacking a pile
of originals;a feeding control unit that controls feeding of originals
from the original tray to a scanning position, the control of feeding of
original including a sheet-through operation in which originals are fed
continuously one by one from the original tray to a scanning position;a
scanning control unit that causes the scanner unit to be fixed at the
scanning position so as to scan originals that pass over the scanning
position when the originals are fed from the original tray;a white plate
provided in a position different from the scanning position;a shading
operation unit that performs a shading operation, the shading operation
including moving the scanner unit to the position of the white plate, and
scanning the white plate to acquire white data to be used in performing
shading correction on image data acquired by the scanner unit; anda
measuring unit that performs a light-quantity measuring operation, the
light-quantity measuring operation including causing the scanner unit to
measure a light quantity of an exposure lamp that illuminates the
original at the scanning position, whereinwhen a pile of originals is
placed on the original tray, the feeding control unit performs the
sheet-through operation,when one original is fed from the original tray
to the scanning position, the shading operation unit performs the shading
operation to acquire current white data, the measuring unit performs the
light-quantity measuring operation to acquire current light quantity of
the exposure lamp as a reference value,when a subsequent original is fed
from the original tray to the scanning position, the measuring unit
performs the light-quantity measuring operation to acquire current light
quantity of the exposure lamp as a subsequent light quantity, andwhen an
amount of change between the reference value and the subsequent light
quantity is out of a predetermined range, the shading operation unit
performs the shading operation to acquire new white data and updates
existing white data with the new white data, the measuring unit performs
the light-quantity measuring operation to acquire new light quantity and
updates existing light quantity with the new light quantity, andthe
feeding control unit does not stop the sheet-through operation when the
shading operation unit is not to perform the shading operation, and the
feeding control unit stops the sheet-through operation when the shading
operation unit is to perform the shading operation.

2. The image reading apparatus according to claim 1, whereinwhen the
shading operation unit is not to perform the shading operation, the
feeding control unit sets so as to disable stopping of the sheet-through
operation at the time of starting of the sheet-through operation, andwhen
the shading operation unit is to perform the shading operation, the
feeding control unit sets so as to enable stopping of the sheet-through
operation at the time of starting of the sheet-through operation.

3. The image reading apparatus according to claim 1, whereinwhen the
shading operation unit is not to perform the shading operation, the
feeding control unit triggers starting of the sheet-through operation
before the sheet-through operation is decelerated, andwhen the shading
operation unit is to perform the shading operation, the feeding control
unit triggers starting of the sheet-through operation after the
sheet-through operation is stopped.

4. The image reading apparatus according to claim 2, further comprising a
switching unit that switches whether nor not the sheet-through operation
is executed.

5. The image reading apparatus according to claim 3, further comprising a
switching unit that switches whether nor not the sheet-through operation
is executed.

6. The image reading apparatus according to claim 2, further comprising a
unit that inhibits a nonstop feeding operation in the sheet-through
operation.

7. The image reading apparatus according to claim 3, further comprising a
unit that inhibits a nonstop feeding operation in the sheet-through
operation.

9. An image reading method enforced on an image reading apparatus, the
image reading apparatus includinga scanner unit configured to scan an
original and acquire image data;an original tray for stacking a pile of
originals;a feeding control unit that controls feeding of originals from
the original tray to a scanning position, the control of feeding of
original including a sheet-through operation in which originals are fed
continuously one by one from the original tray to a scanning position;a
scanning control unit that causes the scanner unit to be fixed at the
scanning position so as to scan originals that pass over the scanning
position when the originals are fed from the original tray;a white plate
provided in a position different from the scanning position;a shading
operation unit that performs a shading operation, the shading operation
including moving the scanner unit to the position of the white plate, and
scanning the white plate to acquire white data to be used in performing
shading correction on image data acquired by the scanner unit; anda
measuring unit that performs a light-quantity measuring operation, the
light-quantity measuring operation including causing the scanner unit to
measure a light quantity of an exposure lamp that illuminates the
original at the scanning position, the image reading method
comprising:when a pile of originals is placed on the original tray, the
feeding control unit performing the sheet-through operation,when one
original is fed from the original tray to the scanning position, the
shading operation unit performing the shading operation to acquire
current white data, the measuring unit performing the light-quantity
measuring operation to acquire current light quantity of the exposure
lamp as a reference value,when a subsequent original is fed from the
original tray to the scanning position, the measuring unit performing the
light-quantity measuring operation to acquire current light quantity of
the exposure lamp as a subsequent light quantity, andwhen an amount of
change between the reference value and the subsequent light quantity is
out of a predetermined range, the shading operation unit performing the
shading operation to acquire new white data and updates existing white
data with the new white data, the measuring unit performing the
light-quantity measuring operation to acquire new light quantity and
updates existing light quantity with the new light quantity, andthe
feeding control unit not stopping the sheet-through operation when the
shading operation unit is not to perform the shading operation, and the
feeding control unit stopping the sheet-through operation when the
shading operation unit is to perform the shading operation.

10. The image reading method according to claim 9, whereinwhen the shading
operation unit is not to perform the shading operation, the feeding
control unit setting so as to disable stopping of the sheet-through
operation at the time of starting of the sheet-through operation, andwhen
the shading operation unit is to perform the shading operation, the
feeding control unit setting so as to enable stopping of the
sheet-through operation at the time of starting of the sheet-through
operation.

11. The image reading method according to claim 9, whereinwhen the shading
operation unit is not to perform the shading operation, the feeding
control unit triggering starting of the sheet-through operation before
the sheet-through operation is decelerated, andwhen the shading operation
unit is to perform the shading operation, the feeding control unit
triggering starting of the sheet-through operation after the
sheet-through operation is stopped.

12. The image reading method according to claim 10, further comprising
setting switching information that that indicates whether nor not the
sheet-through operation is executed.

13. The image reading method according to claim 11, further comprising
setting switching information that that indicates whether nor not the
sheet-through operation is executed.

14. The image reading method according to claim 10, further comprising
inhibiting a nonstop feeding operation in the sheet-through operation.

15. The image reading method according to claim 11, further comprising
inhibiting a nonstop feeding operation in the sheet-through operation.

[0006]Japanese Patent Application Laid-open No. 2005-167854 discloses a
technique for improving productivity of image reading of an original by
performing shading correction most efficiently and correctly depending on
situation and by reducing a reading interval between originals without
deteriorating the quality of a read image. Specifically, if a time Td
between originals, required for performing a sheet-through operation
without stopping, is longer than a shading operating time Ts of a
document feeder (DF), successive reading is performed in a nonstop
operation. When a memory permission notification is notified from a
controller after the sheet-through operation is decelerated, the
sheet-through operation is performed after the memory permission
notification is received. When size reduction of an original is specified
in reading the original, the DF is caused to start the sheet-through
operation when a time T (=Tds-Td) has passed after the memory permission
request is received from the controller, where Tds is a time from
receiving of the memory permission notification to finishing of the
shading correction by the DF.

[0007]Japanese Patent Application Laid-open No. 2002-300394 teaches a
shading correction function facilitating high-speed reading and
minimizing degradation of scan per minute (SPM) to the utmost.
Specifically, when a sheet-through automatic document feeder successively
feeds originals one by one, a shading operation and a light-quantity
measuring operation is performed with respect to the first original. The
shading operation includes stopping the sheet-through operation, scanning
a white plate by using a scanner unit to acquire white data. Shading
correction data is generated from the white data and the shading
correction data is used to perform shading correction of image data
acquired from the originals. The light-quantity measuring operation
includes measuring the light quantity of an exposure lamp that
illuminates originals with the scanner unit. The light quantity data of
the exposure lamp measured in the light-quantity measuring operation
corresponding to the first original is saved as a reference value.

[0008]Even when the setting is such that the shading operation is not to
be performed with respect to the second and subsequent originals, the
light-quantity measuring operation is still performed with respect to
each subsequent original (i.e., the second original to the last original)
thereby acquiring subsequent light quantity data. If the difference
between the reference data and the subsequent light quantity data is out
of a preset range, it means that the conditions have changed whereby the
reference value is no more appropriate. In this situation, the reference
value is updated with the latest subsequent light quantity data.

[0009]FIG. 7 is a flowchart of the process of intermittent shading
correction performed by the image reading apparatus disclosed in Japanese
Patent Application Laid-open No. 2002-300394. The scanner unit performs a
density measuring operation in an interval between sheets of paper (Step
S101). The density measuring operation includes measuring a density of a
member that is provided on the original feeding side. "Interval between
sheets of paper" in this specification means a period between a time
point at which the trailing edge of a preceding original leaves a
scanning position and a time point at which the leading edge of a
subsequent original reaches the scanning position. In other words, in the
density measuring operation the scanner unit measures the density of the
member after the trailing edge of the first original has passed a
scanning position and before a leading edge of the second original
reaches the scanning position. If the preceding original is the first
original, then the measured density is saved as a reference value (Steps
S102 and S103).

[0010]If the preceding original is an original other than the first
original (Step S102), an amount of change is calculated based on the
reference value and the density measured at Step S101 (Step S104). The
amount of change is expressed in percent. An allowable range of the
amount of change is previously determined. It is determined whether the
calculated amount of change is within the allowable range (Step S105). If
the calculated amount of change is within the allowable range, the
process is terminated (YES at Step S105). On the other hand, if the
calculated amount of change is out of the allowable range (NO at Step
S105), it means that the current reference value is no more appropriate
for the current conditions. In this situation, the reference value is
updated (Step S106).

[0011]When updating the reference value, first, an instruction to stop the
sheet-though operation is output (Step S107), so that feeding of
originals is stopped. In this situation, the shading operation is
performed to acquire new white data (Step S108). Upon completion of the
shading operation (Step S109), the existing white data is corrected, or
updated, with the new white data. Finally, an instruction to start the
sheet-though operation is output (Step S110) so that feeding of originals
is started, and the process is terminated. Thereafter, Steps S101 to S110
are repeated for all the originals to be read.

[0012]Japanese Patent Application Laid-open No. 2002-300394 proposes an
image reading apparatus that includes an automatic document feeding
mechanism capable of enhancing productivity by not executing the shading
operation for each original, but by reducing intervals of the shading
operation to thereby reduce a waiting time for the shading operation. It
is suggested that the productivity can be enhanced by optimizing an
interval between originals using arbitrary means based on whether or not
the shading operation is to be executed. Specifically, as understood from
the flowchart in FIG. 7, sheet-through operation (original feeding) is
explicitly stopped (Step S107) before beginning the shading operation,
and the sheet-through operation is restarted after the shading operation
is completed (Step S110). Meanwhile, when the shading operation is not to
be executed (YES at Step S105), i.e., when the calculated amount of
change is within the allowable range, the timing of starting the
sheet-through operation is not certain. Various drawbacks occur if this
timing is not correct. Therefore, the sheet-through operation cannot
always be performed in a nonstop manner, and the productivity cannot
thereby be maximally improved.

[0013]Specifically, as shown in a timing chart in FIG. 8, if the
sheet-through operation is to be performed in a non-stop manner, the
start of sheet-through operation needs to be triggered before a
sheet-through deceleration period L1 starts. Otherwise, the sheet-through
operation cannot be started at a timing T1 at which a sheet-through stop
period L2 is over. However, Japanese Patent Application Laid-open No.
2002-300394 does not disclose about when and how to start the
sheet-through operation when the shading operation is not to be executed,
i.e., when the calculated amount of change is within the allowable range.

[0014]Meanwhile, Japanese Patent Application Laid-open No. 2005-167854
proposes an image reading apparatus capable of enhancing productivity by
comparing a time interval between originals when the originals are fed
nonstop using the automatic document feeder with a time required for the
shading operation, and of feeding the originals nonstop when the shading
time is shorter than the other. Therefore, because the shading time
becomes substantially zero when the shading operation is not executed in
the technology disclosed in Japanese Patent Application Laid-open No.
2002-300394, a nonstop operation determination mechanism described in
Japanese Patent Application Laid-open Nos. 2005-167854 is used to feed
the originals nonstop, which can achieve improvement of the productivity.

[0015]However, in the document feeder, when the trigger of the start of
sheet-through operation is received before the sheet-through operation is
decelerated, the sheet-through operation is performed nonstop, and when
the trigger is received after the sheet-through operation is decelerated,
the operation is performed with deceleration of the sheet-through
operation and stop of the sheet-through operation. Therefore, to switch
between operations so that the nonstop sheet-through operation is
performed when the shading operation is not executed and the stop
operation is performed when it is executed, it is necessary to provide a
mechanism to explicitly switch to the sheet-through operation.

SUMMARY OF THE INVENTION

[0016]It is an object of the present invention to at least partially solve
the problems in the conventional technology.

[0017]According to an aspect of the present invention, there is provided
an image reading apparatus including a scanner unit configured to scan an
original and acquire image data; an original tray for stacking a pile of
originals; a feeding control unit that controls feeding of originals from
the original tray to a scanning position, the control of feeding of
original including a sheet-through operation in which originals are fed
continuously one by one from the original tray to a scanning position; a
scanning control unit that causes the scanner unit to be fixed at the
scanning position so as to scan originals that pass over the scanning
position when the originals are fed from the original tray, and a white
plate provided in a position different from the scanning position; a
shading operation unit that performs a shading operation, the shading
operation including moving the scanner unit to the position of the white
plate, and scanning the white plate to acquire white data to be used in
performing shading correction on image data acquired by the scanner unit;
and a measuring unit that performs a light-quantity measuring operation,
the light-quantity measuring operation including causing the scanner unit
to measure a light quantity of an exposure lamp that illuminates the
original at the scanning position. When a pile of originals is placed on
the original tray, the feeding control unit performs the sheet-through
operation, when one original is fed from the original tray to the
scanning position, the shading operation unit performs the shading
operation to acquire current white data, the measuring unit performs the
light-quantity measuring operation to acquire current light quantity of
the exposure lamp as a reference value, when a subsequent original is fed
from the original tray to the scanning position, the measuring unit
performs the light-quantity measuring operation to acquire current light
quantity of the exposure lamp as a subsequent light quantity. When an
amount of change between the reference value and the subsequent light
quantity is out of a predetermined range, the shading operation unit
performs the shading operation to acquire new white data and updates
existing white data with the new white data, the measuring unit performs
the light-quantity measuring operation to acquire new light quantity and
updates existing light quantity with the new light quantity, and the
feeding control unit does not stop the sheet-through operation when the
shading operation unit is not to perform the shading operation, and the
feeding control unit stops the sheet-through operation when the shading
operation unit is to perform the shading operation.

[0018]According to another aspect of the present invention, there is
provided an image forming apparatus that includes the above image reading
apparatus.

[0019]According to still another aspect of the present invention, there is
provided an image reading method enforced on an image reading apparatus.
The image reading apparatus including a scanner unit configured to scan
an original and acquire image data; an original tray for stacking a pile
of originals; a feeding control unit that controls feeding of originals
from the original tray to a scanning position, the control of feeding of
original including a sheet-through operation in which originals are fed
continuously one by one from the original tray to a scanning position; a
scanning control unit that causes the scanner unit to be fixed at the
scanning position so as to scan originals that pass over the scanning
position when the originals are fed from the original tray; a white plate
provided in a position different from the scanning position; a shading
operation unit that performs a shading operation, the shading operation
including moving the scanner unit to the position of the white plate, and
scanning the white plate to acquire white data to be used in performing
shading correction on image data acquired by the scanner unit; and a
measuring unit that performs a light-quantity measuring operation, the
light-quantity measuring operation including causing the scanner unit to
measure a light quantity of an exposure lamp that illuminates the
original at the scanning position. The image reading method including,
when a pile of originals is placed on the original tray, the feeding
control unit performing the sheet-through operation, when one original is
fed from the original tray to the scanning position, the shading
operation unit performing the shading operation to acquire current white
data, the measuring unit performing the light-quantity measuring
operation to acquire current light quantity of the exposure lamp as a
reference value, when a subsequent original is fed from the original tray
to the scanning position, the measuring unit performing the
light-quantity measuring operation to acquire current light quantity of
the exposure lamp as a subsequent light quantity, and when an amount of
change between the reference value and the subsequent light quantity is
out of a predetermined range, the shading operation unit performing the
shading operation to acquire new white data and updates existing white
data with the new white data, the measuring unit performing the
light-quantity measuring operation to acquire new light quantity and
updates existing light quantity with the new light quantity, and the
feeding control unit not stopping the sheet-through operation when the
shading operation unit is not to perform the shading operation, and the
feeding control unit stopping the sheet-through operation when the
shading operation unit is to perform the shading operation.

[0020]According to still another aspect of the present invention, there is
provided an image forming method including the image reading method.

[0021]The above and other objects, features, advantages and technical and
industrial significance of this invention will be better understood by
reading the following detailed description of presently preferred
embodiments of the invention, when considered in connection with the
accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic diagram of a configuration of an image reading
apparatus and a time chart of a scanning operation according to an
embodiment of the present invention;

[0023]FIG. 2 is a functional block diagram of a control system of the
image reading apparatus for explaining flow of signals;

[0024]FIG. 3 is a flowchart of an example of a control process executed by
the image reading apparatus;

[0025]FIG. 4 is a block diagram of a conceptual system configuration of an
image forming apparatus that includes the image reading apparatus;

[0026]FIG. 5 is a flowchart of another example of a control process
executed by the image reading apparatus;

[0027]FIG. 6 is a flowchart of still another example of a control process
executed by the image reading apparatus;

[0028]FIG. 7 is a flowchart of a control process executed by a
conventional image reading apparatus; and

[0029]FIG. 8 is a timing chart representing a timing of a deceleration
period when an original is fed and a timing of a stop period, which are
executed based the conventional technology.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030]Exemplary embodiments of the present invention are explained in
detail below with reference to the accompanying drawings.

[0031]FIG. 1 is a schematic diagram of an image reading apparatus 1 and a
time chart of a scanning operation according to an embodiment of the
present invention. Two modes of original feeding are possible in the
image reading apparatus 1: one is manual-feed mode in which an original
is manually placed on a contact glass and the other is auto-feed mode in
which an original is set in an automatic document feeder. FIG. 2 is a
functional block diagram of a control system of the image reading
apparatus 1.

[0032]A hardware configuration of the image reading apparatus 1 is almost
the same as that of a typical image reading apparatus. Namely, in the
manual-feed mode, the original set on a contact glass 2 is irradiated
with a light beam from an exposure lamp 3 provided in a first carriage 4.
The light reflected from the surface of the original is then reflected
from mirrors provided in a second carriage 5 and converged with lens 6
and focused onto a CCD 7. The first carriage 4 and the second carriage 5
are moved so as to scan the surface of the original thereby "reading" the
original and acquiring image data of the original. The exposure lamp 3
can be fluorescent lamp. The CCD 7 is mounted on a scanner board unit
(SBU). The CCD 7 can be some other image sensor. The first carriage 4 and
the second carriage 5 are driven by a scanner motor 11.

[0033]The image data is typically subjected to shading correction in order
to improve the image quality. The shading correction is performed based
on the shading data acquired by assuming white as a reference color. For
this purpose, a white plate 8 is provided in the image reading apparatus
1. The first carriage 4 and the second carriage 5 are moved so as to scan
the white plate 8 and acquire white data.

[0034]When beginning the operation of reading the original placed on the
contact glass 2, the exposure lamp 3 is turned on, and the first and the
second carriages 4 and 5 are moved at a preset constant speed, and first
the white plate 8 is read and white data is collected while an SHGATE
signal is active. After reading of the white plate 8 is completed, the
first carriage 4 is moved to a scanning position 12 of the original and
the original is read while an FGATE signal is active while moving the
first and the second carriages 4 and 5 at a preset constant speed. After
the entire original is read, the first and the second carriages 4 and 5
are returned to their initial positions.

[0035]The scanning position 12 is provided in the upstream side of the
white plate 8. Specifically, as illustrated in FIG. 1, the scanning
position 12 is provided on the left side of the white plate 8.

[0036]A sheet-through automatic document feeder (hereinafter, "ADF") 100
includes the original tray 101, a pickup roller 102, the feed drum 103, a
pair of feed rollers 104, a pair of paper ejection rollers 105, and a
paper ejection tray 106. The ADF 100 is fixed to the top surface of an
image reading apparatus 1 in an openable/closable manner. Set on the
original tray 101 is a stack of originals that are to be scanned. When
the sheet-through operation is started, the originals are picked up one
by one from the top thereof by the pickup roller 102 and are sent to the
feed drum 103. The originals are sent to the scanning position 12 along a
feed path 107 while being held between the feed rollers 104 and
sandwiched between the feed rollers 104 and the feed drum 103, scanned
when they reach the scanning position 12, and ejected by the paper
ejection rollers 105 onto the paper ejection tray 106.

[0038]The scanning operation in the manual-feed mode is briefly explained
below. In the manual-feed mode, an original is placed on the contact
glass 2. In the following explanation, "to assert" means rising of a
signal which means a start of a process, and "to negate" means returning
of the signal to its former state which means an end of the process.
"White data is normal" means that, when a white side of 8-bit image data
is assumed to be 255 and a black side thereof is assumed to be 0, the
white data is close to 255.

[0039]When receiving "scan start information", the sub-scanning timing
generator 203 resets an abnormality flag, turns on the exposure lamp 3,
and causes the scanner motor 11 to drive a scanner unit that includes the
first and the second carriages 4 and 5. When the first carriage 4 reaches
the position for scanning the white plate 8, an SLEAD signal is asserted.
The scanner unit scans the white plate 8 while the SLEAD signal is
asserted and acquires white data, and transmits the white data to the
image processor 201. The image processor 201 calculates the shading data
from the white data.

[0040]When the first carriage 4 leaves the area of the white plate 8 and
reaches a position of negating the SLEAD signal, the SLEAD signal is
negated, and the sub-scanning timing generator 203 loads the white data.
If the value of the white data is close to the value of white, i.e., 255,
the image scanning process is continued. When the first carriage 4
reaches a scanning position of the original that is placed on the contact
glass 2, an SSCAN signal is asserted, and image scanning process is
performed in a usual manner. If the value of the white data is not close
to the value of white, i.e., 255, the SSCAN signal (FGATE signal) is not
generated so as to prevent the process of scanning the original data.
Thus, abnormal original data is not sent to the image processor 201, so
that an output of the abnormal image can be prevented. The shading data
generating/updating unit 2011 calculates new shading data from the white
data and updates the existing shading data with the new shading data.

[0041]The scanning operation in the auto-feed mode is briefly explained
below. In the auto-feed mode, an original is set on the original tray
101. In the state that the original is set on the original tray 101, and
a scan start instruction is received, the shading operation is performed
first. Specifically, the first carriage 4 moves to a position to scan the
white plate 8, scans the white plate 8 and acquires white data, saves the
white data, and returns to the scanning position 12 for the sheet-through
operation. The shading data generating/updating unit 2011 calculates new
shading data from the white data and updates the existing shading data
with the new shading data. After the first carriage 4 returns to the
scanning position 12, one original set on the original tray 101 is fed to
the scanning position 12 and scanned to acquire image data. This original
is then discharged into paper ejection tray 106 by the paper ejection
rollers 105 and the next original is fed to the scanning position 12 from
the original tray 101 and scanned to acquire image data. The image data
is subjected to the shading correction by using the shading data.

[0042]Flow of the signals is shown in FIG. 2. The sub-scanning timing
generator 203 receives the scan start information, drives the scanner
motor 11, and outputs the SLEAD signal indicating an area of scanning the
white plate 8 to the scanning unit 202. The scanning unit 202 receives
the signal, acquires line-synchronization (LSYNC) of the signal with a
signal corresponding to an actual white-plate scanning position, and
outputs the signal as an SHGATE signal to the image processor 201. The
scanner unit reads the density of the white plate 8 during a period in
which the SHGATE signal asserted to generate white data. When the shading
operation is finished, the scanner unit returns to the scanning position
for the sheet-through operation.

[0043]Next, the ADF 100 receives "original feeding start" information, and
starts feeding the originals set on the original tray 101 one by one.
When an original reaches the scanning position 12, the ADF 100 outputs
the SSCAN signal. The scanning unit 202 acquires line-synchronization
with the SSCAN signal, and outputs the FGATE signal to the image
processor 201. When the trailing edge of the original passes through the
scanning position 12, a DFEND signal is negated. A *SHGT signal is
generated when the trailing edge of the original passes through the
scanning position 12, and a logical AND operation is executed between
*SHGT and SHGT. By doing this, the scanning unit 202 can calculate when
to start and finish the density measuring operation in an interval
between sheets of paper. The density measuring operation includes
measuring a density of a member that is provided on the original feeding
side. The interval between sheets of paper means a period between a time
point at which the trailing edge of a preceding original leaves the
scanning position 12 and a time point at which the leading edge of a
subsequent original reaches the scanning position 12. The member provided
on the original feeding side can be a white-color feed drum or a white
plate other than the white plate 8. A guide plate (not shown) used to
bring an original into tight contact with a glass window at the scanning
position 12 can be used as the member. Although the member provided on
the original feeding side is scanned in the interval between sheets of
paper, the reference value is not updated with the data acquired from
this member. With this control, a signal is generated so as to be reset
when the SLEAD signal is asserted and so as to be preset with the DFEND
signal, and the reference value is updated based on the signal.

[0044]The shading correction is performed to correct the change in a
scanning level due to changes in distribution characteristics and the
light quantity in the main scanning direction of the exposure lamp, and
dirt on the white plate, dirt on mirrors, and dirt on the contact glass
in the scanning position 12. The purpose of performing the shading
correction for each original is mainly to counter the change in light
amount of the exposure lamp. Furthermore, there is individual difference
in stability of the light amount after turn-on of the exposure lamp is
started, or there is a difference depending on the light source, so that
characteristic of the exposure lamp are not stable.

[0045]In the conventional technology, as shown in the flowchart of FIG. 7
and in the timing chart of FIG. 8, the reference value is acquired for
the first original by performing the density measuring operation, and
only the density of the member provided on the original feeding side is
measured for the second and subsequent originals in the interval between
sheets of paper. If the measured density and the reference value do not
deviate greatly, i.e., if the amount of change between the measured
density and the reference value is within an allowable range regarded as
that the change will affect the quality of the images, the reference
value is not updated. Meanwhile, if the amount of change is such that it
will affect the quality of images, the shading operation is performed to
measure new density and the reference value is updated with the new
density.

[0046]On the other hand, in the embodiment, when the shading operation is
not to be executed, i.e., when the amount of change is within the
allowable range, the trigger of the start of sheet-through operation is
given at the timing before the sheet-through operation is decelerated or
before it is stopped, and this trigger causes the originals to be fed in
a nonstop manner. The procedure at this time is shown in the flowchart of
FIG. 3.

[0047]This flowchart is different from the flowchart shown in FIG. 7
according to the conventional technology in only one point. The
difference is what happens at Step S105 when the amount of change is
within the allowable range. Specifically, when the amount of change is
within the allowable range (YES at step S105) an instruction to start
original feeding operation is output (Step S111) at a timing that is
before the sheet-through deceleration period L1 shown in FIG. 8 starts.
The scanner unit performs a density measuring operation in an interval
between sheets of paper (Step S101). The density measuring operation
includes measuring a density of a member that is provided on the original
feeding side. If the preceding original is the first original, then the
measured density is saved as a reference value (Steps S102 and S103). If
the preceding original is an original other than the first original (Step
S102), an amount of change is calculated based on the reference value and
the density measured at Step S101 (Step S104). The amount of change is
expressed in percent. An allowable range of the amount of change that
will not affect the image quality is previously determined. It is
determined whether the calculated amount of change is within the
allowable range (Step S105). If the amount of change is within the
allowable range (YES at Step S105), an instruction to start original
feeding operation is output and the process is terminated (Step S111). On
the other hand, if the calculated amount of change is out of the
allowable range (NO at Step S105), it means that the current reference
value is no more appropriate for the current conditions. In this
situation, the reference value is updated (Step S106).

[0048]When updating the reference value, first, an instruction to stop the
sheet-though operation is output (Step S107), so that feeding of
originals is stopped. In this situation, the shading operation is
performed to acquire new white data (Step S108). Upon completion of the
shading operation (Step S109), the existing white data is corrected, or
updated, with the new white data. Finally, an instruction to start the
sheet-though operation is output (Step S110) so that feeding of originals
is started, and the process is terminated. Thereafter, Steps S101 to S110
are repeated for all the originals to be read. The shading data
generating/updating unit 2011 calculates new shading data from the white
data and updates the existing shading data with the new shading data.

[0049]In this case, with reference to FIG. 4, the timing when the trigger
of the start of sheet-through operation can be given is immediately after
the timing when the scanning unit 202 receives the memory permission
notification from the image processor (controller) 201, or is arbitrary
timing thereafter. FIG. 4 is a block diagram of a conceptual
configuration of an image forming apparatus that includes the image
reading apparatus 1. In FIG. 4, reference numeral 205 represents an image
output unit, and 200 represents an operation request source (e.g.,
application).

[0050]By performing the process in the above manner, the sheet-through
operation can be performed in a nonstop manner when the shading operation
is not executed. This enables to improve scanning productivity.

[0051]In the flowchart of FIG. 3, the nonstop operation is realized by
instructing to start feeding of the next original at Step S111. However,
the nonstop operation can be realized with some other method. For
example, to switch between the nonstop operation and the stop operation,
"nonstop" and "stop" settings can be provided, and, if "nonstop" is set,
a trigger of a next start of sheet-through operation is output at the
timing before the sheet-through operation is decelerated or before it is
stopped. FIG. 5 is a flowchart of an example of previously setting
whether the nonstop operation is to be executed.

[0052]As shown in FIG. 5, the scanner unit performs a density measuring
operation in an interval between sheets of paper (Step S101). The density
measuring operation includes measuring a density of a member that is
provided on the original feeding side. If the preceding original is the
first original, then the measured density is saved as a reference value
(Steps S102 and S103). If the preceding original is an original other
than the first original (Step S102), an amount of change is calculated
based on the reference value and the density measured at Step S101 (Step
S104). The amount of change is expressed in percent. An allowable range
of the amount of change is previously determined. It is determined
whether the calculated amount of change is within the allowable range
(Step S105). If the calculated amount of change is within the allowable
range (YES at Step S105), the setting of "original feed stop" is disabled
(Step S125), and then an instruction to start original feeding operation
is output (Step S126). When feeding of the next original is started (Step
S124), the process is terminated.

[0053]On the other hand, if the calculated amount of change is out of the
allowable range (NO at Step S105), it means that the current reference
value is no more appropriate for the current conditions. In this
situation, the reference value is updated (Step S106).

[0054]When updating the reference value, the setting of the original feed
stop is enabled (Step S121), an instruction to start original feeding
operation is output (Step S122), the shading operation is performed to
acquire new white data while the original feed stop is in enabled state,
and the existing white data is corrected, or updated, with the new white
data (Step S123). Finally, feeding of originals is started at the timing
T1 shown in FIG. 8 (Step S124), and the process is terminated.
Thereafter, Steps S101 to S124 are repeated for all the originals to be
read. The shading data generating/updating unit 2011 calculates new
shading data from the white data and updates the existing shading data
with the new shading data.

[0055]Thus, the stop operation can be implemented when the shading
operation is executed, and the stop operation can be switched to the
nonstop operation when the shading operation is not executed. This
enables improvement of the scanning productivity while maintaining the
image quality.

[0056]In the flowchart of FIG. 3, as explained above, the nonstop
operation is instructed by instructing the original feeding start at Step
S111, however, to switch between the nonstop operation and the stop
operation, for the nonstop operation, by triggering a next start of
sheet-through operation at the timing before the sheet-through operation
is decelerated or before it is stopped, the nonstop operation is
performed, and for the stop operation, by triggering a start of
sheet-through operation after the sheet-through operation is stopped, the
stop operation can also be performed. FIG. 6 is a flowchart of an example
of starting the sheet-through operation after an original is stopped when
the nonstop operation is not executed.

[0057]In this example, the process to be performed when the amount of
change is within the allowable range at Step S105 is different from that
of the flowchart shown in FIG. 5. Specifically, when the amount of change
is within the allowable range at Step S105 (YES at Step S105), an
instruction to start original feeding operation is output at Step S127.
This enables the process to continue without stopping the original. The
rest of the process is the same as that explained with reference to the
flowchart in FIG. 5.

[0058]By performing the processes in the above manner, the stop operation
can be implemented when the shading operation is executed, and the stop
operation can be switched to the nonstop operation when the shading
operation is not executed. Thus, the scanning productivity can be
improved while maintaining the image quality.

[0059]In the image reading apparatus that controls switching between stop
and nonstop operations of the sheet-through operation according to
whether the shading operation is to be executed or not, the original
easily skews at the time of the nonstop operation, and, this may result
in a decrease in the quality of an image scanned through the nonstop
operation. As a countermeasure against this problem, when the image
quality is to be given preference over the productivity, it is desirable
to enable scanning with the stop operation at any time by inhibiting
scanning with the nonstop operation.

[0060]Therefore, as shown in FIG. 4, an operation display unit 206 is
provided as a user interface through which the user can set whether or
not the nonstop operation is to be executed in the CPU 2010 of the image
processor (controller) 201, so that it can be switched, according to the
result of user selection, whether or not the nonstop operation is
executed. Consequently, the user can set either one of the operations by
operating a selection key to select the operation through the operation
display unit 206. At this time, user settings are stored in a nonvolatile
storage, for example, in a recording medium 207 such as a memory
controlled by the CPU 2010. With this feature, whether or not the nonstop
operation is executed can be switched based on a set content even after
the power is on or off. Because the user can set the execution or the
non-execution of the nonstop operation in the above manner, degradation
of image quality can be prevented. At this time, because information for
the execution or the non-execution of the nonstop operation set by the
user can be stored, another setting of the information required at the
time of the power ON can be eliminated, which allows for improved
usability.

[0061]The image reading apparatus may also be configured to detect by
itself how the original skews, permit scanning with the nonstop operation
before the skew occurs, and inhibit scanning with the nonstop operation
after the skew occurs. Detection of the skew is not particularly shown in
the figures. However, the detection is implemented by comparing the
length of a size detected by an original-size detection mechanism with
that of an original size obtained by being inversely calculated from
output times of detection signals of an original detection sensor that
detects an original while being fed (signal being ON when the leading
edge of the original is detected, and signal being OFF when the trailing
edge thereof passes). It is determined based on the comparison that the
skew has occurred if the length is different from the original size by a
predetermined length or more. Based on this determination, the operation
can be automatically switched to the stop operation upon occurrence of
the skew, so that images can be provided to the user without degradation
of image quality.

[0062]It goes without saying that the present invention is not limited to
the embodiment, but covers all the technical items in the technical idea
described in the scope of the claims.

[0063]According to an aspect of the present invention, improved scanning
productivity can be achieved while maintaining the image quality.

[0064]Although the invention has been described with respect to specific
embodiments for a complete and clear disclosure, the appended claims are
not to be thus limited but are to be construed as embodying all
modifications and alternative constructions that may occur to one skilled
in the art that fairly fall within the basic teaching herein set forth.